O'Fallon's history as a city started in the 1850s. Arnold Krekel was a German immigrant who held a number of offices, including U.S. District Court Judge and Missouri state legislator. He founded a German-language newspaper and invested in the North Missouri Railroad, among other activities. Krekel's younger brother Nicholas built the first house in O'Fallon and is considered by many to be the "founder" of O'Fallon. The younger Krekel was the town's first Postmaster, station agent, and operated the first general merchandise store inside his home. The City purchased this historic house in 2008 with plans for restoration after which it will be open to the public.

In 1854, Judge Krekel granted the North Missouri Railroad permission to build a depot on his property along with a right-of-way on his "Krekel Addition". In 1856, Judge Krekel named the depot O'Fallon Station after his friend John O'Fallon,[11] the railroad's president and a noted philanthropist. In 1860, the "Krekel Addition" was renamed O'Fallon, and in 1912, it was incorporated.

For many years, O'Fallon was a quiet, small community in central St. Charles County. In the early 1980s suburban development accelerated and a population boom began. The population for O'Fallon rose to 18,698 by 1990, and was more than 70,000 residents by 2006.

According to the United States Census Bureau, the city has a total area of 29.20 square miles (75.63 km2), of which, 29.19 square miles (75.60 km2) is land and 0.01 square miles (0.03 km2) is water.[2]

There were 28,234 households of which 44.7% had children under the age of 18 living with them, 61.6% were married couples living together, 10.0% had a female householder with no husband present, 4.3% had a male householder with no wife present, and 24.1% were non-families. 19.3% of all households were made up of individuals and 6.2% had someone living alone who was 65 years of age or older. The average household size was 2.80 and the average family size was 3.23.

The median age in the city was 34.3 years. 30% of residents were under the age of 18; 7.1% were between the ages of 18 and 24; 30.8% were from 25 to 44; 23.1% were from 45 to 64; and 8.9% were 65 years of age or older. The gender makeup of the city was 48.8% male and 51.2% female.

There are 15,389 households out of which 50.6% have children under the age of 18 living with them, 69.8% are married couples living together, 8.6% have a female householder with no husband present, and 18.1% are non-families. 14.1% of all households are made up of individuals and 3.4% have someone living alone who is 65 years of age or older. The average household size is 2.98 and the average family size is 3.30.

In the city the population is spread out with 33.4% under the age of 18, 6.4% from 18 to 24, 38.8% from 25 to 44, 15.3% from 45 to 64, and 6.2% who are 65 years of age or older. The median age is 31 years. For every 100 females there are 97.3 males. For every 100 females age 18 and over, there are 95.1 males.

The median income for a household in the city is $60,179, and the median income for a family is $64,627. Males have a median income of $45,295 versus $29,129 for females. The per capita income for the city is $21,774. 3.3% of the population and 2.6% of families are below the poverty line. Out of the total population, 3.3% of those under the age of 18 and 6.7% of those 65 and older are living below the poverty line.

O'Fallon is home to MasterCard's Global Technology and Operations center, where MasterCard's credit-card transactions are settled. Attracting that center cost the city, county, and state:[citation needed]

O'Fallon operates under a charter form of government. In 2010, the current four wards were redistricted and a new, fifth ward was created. The current mayor is William "Bill" Hennessy. The current (February 2014) City Council members are: Bill Gardner, Rick Lucas, Rose Mack, Jim Pepper, John Haman, Rick Batelle, Jeff Schwentker, Bob Howell, and Mike Pheney. The City Administrator is Bonnie Therrien.

Laws

Proposition S

On April 5, 2011, 72% of O'Fallon voters approved of Proposition S, the "Smoke-Free O'Fallon" Ordinance. The ordinance became a law and went into effect on June 16, 2011. Under the new law, there is a ban on smoking in all places of employment and at indoor public events. Some examples of places of employment that are under the smoking ban include libraries, schools, bars, restaurants, stores, manufacturers and private clubs who either have employees or host public events. In addition to the smoking ban at places of employment, there should also be proper “No Smoking” signs posted at every entrance of places of employment, and no ashtray should be in the smoke-free areas at places of employment. There are some exclusions in the ordinance, including: private homes, 20% of hotel and motel rooms, outdoor events, and outdoor spaces more than 3 feet away from doorways, windows, and ventilation systems.[18]

Fire Protection is mostly provided by the O'Fallon Fire Protection District which in 2007 became the first Internationally Accredited Fire Agency in the State of Missouri. The award was made by the Center for Public Safety Excellence's Commission on Fire Accreditation International (CFAI). The CFAI has approved accreditation status for only 120 fire agencies world wide.